This invention pertains to dissociating H2O into hydrogen and oxygen. More particularly it pertains to splitting H2O into hydrogen and oxygen in a process wherein a hydrocarbon fuel acts as an initiator and the dissociation takes place under non-equilibrium thermal plasma conditions after the fuel and H2O are uniformly mixed and heated using rotating flow.
Hydrogen powered fuel cells have long been recognized as having great potential for stationary power generation and for transportation applications. Advantages of fuel cells include their ability to generate power more efficiently than internal combustion engines and other conventional power sources while producing essentially no pollutants. However, currently, no scalable, cost-effective, environmentally attractive hydrogen production process is available for commercialization. Hydrogen can be produced from dissociation of H2O or from reforming of hydrogen fuels. Dissociation of H2O is ideal from an environmental perspective because it produces no greenhouse gases; dissociation of H2O through electrolysis is energy-intensive and prohibitively expensive.
Hydrogen can be produced from hydrocarbon fuels with use of conventional technologies such as steam reforming, partial oxidation, and auto-thermal reforming. However, these technologies tend to require large components and to be not efficient in meeting large demands, a disadvantage for space-limited facilities such as fueling stations. There are also several technical issues such as capability for fast starts, sulfur contamination, and soot or carbon formation. One problem common to conventional reforming is sulfur removal. Conventional reformer technology requires removal of sulfur from liquid fuels, which is usually accomplished with use of catalysts and heavy heaters. Such components usually raise gas poisoning and temperature sensitivity issues. Also in conventional reformer technology, poor fuel dispersion will create uneven fuel distribution and result in carbon/coke formation in fuel-rich zones and hot spots in fuel-lean zones. The U.S. Department of Energy (USDOE) estimates that currently it costs between $5.00 and $6.00 to produce a kilogram of hydrogen, and that this cost should be reduced to $1.50/kg to be competitive with conventional fuels. The USDOE has also set a primary energy efficiency of 75% to be met in the year 2010. The efficiency of conventional technology for producing hydrogen currently ranges between 65% and 80%.
It is difficult to dissociate H2O because very high temperatures, in excess of 2500° C., are needed. Also, it is difficult to ionize H2O because it has a higher ionization energy and enthalpy formations of ions (12.6 eV and 976 kJ/mol, respectively) than hydrocarbon fuels of interest. For example, gasoline has an ionization energy of 9.8 eV and an enthalpy formation of ions of 737 kJ/mol. In addition, it is difficult to ionize H2O using high energy electrons because H2O is a small molecule that has a small cross section for ionization by high energy (hard) electrons. However, H2O cross section for ionization is larger for low energy (soft) electrons than for hard electrons. Such an environment can be created in a reactor in which plasma conditions are set up when hydrocarbon fuels and H2O are heated to temperatures in the range of 700° C. to 1,000° C.
Wang has taught the use of a reactor for the chemical destruction of heavy-molecule volatile organic compounds, semi-volatile organic compounds, or hydrogen sulfide in U.S. Pat. No. 5,614,146. In such a reactor, the energy to produce plasma and maintain high temperatures comes from the fuel and from electric sources. Thermal radiation enhancement and energy trapping techniques are also used to minimize heat loss. Electro-magnetic hydrodynamics (EMHD) flow creates non-equilibrium chemical reaction conditions to minimize recombination and the conversion or reforming rates. Wang and Lyons in U.S. Pat. No. 6,458,478 B1 have taught the use of such a reactor in an integrated system for producing electricity in a fuel cell for stationary or electric-powered vehicle applications.
The reactor taught by Wang above has been improved to make it efficient for dissociating H2O (see U.S. Pat. No. 7,070,634 B1). Electrons generated at a hot electrode surface flow toward a cold electrode surface. Interaction between electrons and molecules of a steam/hydrocarbon gas flow generates ionization plasma and increases conductivity of the gas flow. Owing to continued fuel/H2O feeding, thermal expansion and the EMHD forces, the plasma flow is being pushed downstream and forms a plasma volumetric flow swept through the entire reactor volume.
Although it is preferred that the dissociation occur in the type of plasma reformer described above, the use of a plasma reformer to produce hydrogen rich gas is taught is discussed by Cohn, et al. in U.S. Pat. No. 5,887,554 and by Bromberg et al. in U.S. Pat. No. 5,409,784. The use of a plasma reactor with microwave energies for the production of hydrogen from dissociation of hydrogen sulfide is taught by Harkness et al in U.S. Pat. No. 5,211,923. Also, conventional technologies such as steam reformers, partial oxidation reformers and autothermal reformers could be used.